This application relates to disc drives and more particularly to an apparatus and method for gathering data to detect a defect in a magneto-resistive head in a disc drive.
Disc drives store data by creating localized magnetic fields on one or more flat, circular discs within the disc drive. Thus, the discs within the disc drive serve as a recording medium, and the localized magnetic fields serve as the means by which data are represented. Reading data that have been stored by a disc drive requires that the localized magnetic fields be detected, so that the data they represent can be reconstructed.
The localized magnetic fields can be detected by several mechanisms. One particular mechanism that is well suited for detecting the presence of a localized magnetic field is a magneto-resistive head. A magneto-resistive head is a small, magnetically sensitive element that changes its resistance when in the presence of variable magnetic flux. Accordingly, by orienting a magneto-resistive head over a spinning disc, the magneto-resistive head will detect the presence of localized magnetic fields stored on the disc spinning beneath it. By orienting the magneto-resistive head at a given distance from the center of the disc, the data stored along the particular circular path passing under the head (called a xe2x80x9ctrackxe2x80x9d) will be read.
The magnetically sensitive element within a magneto-resistive head is called a xe2x80x9cmagnetic stripe.xe2x80x9d A magnetic stripe typically has a width about 80% of that of the track it is reading. Thus, the entire magnetic stripe is immersed in a particular localized magnetic field when the field is oriented, i.e., passes beneath, the magnetic stripe, and it is important that no portion of the magnetic stripe become damaged, lest the magneto-resistive head lose its ability to read the data stored upon the disc.
A magneto-resistive stripe is particularly sensitive to electrostatic discharges. A significantly low electrical potential can damage a magnetic stripe. Since electrostatic potentials may develop during the course of certain manufacturing operations (electrostatic potentials develop when two non-conducting materials rub together), it is important that a test be developed to monitor the damage sustained by the magnetic stripes over the course of their manufacture. Additionally, it is desirable that a test be developed which can be performed with the disc drive fully assembled, so as not to require the disassembly or destruction of the disc drive under test. Testing a fully assembled drive permits a magneto-resistive head to be examined inexpensively, and without introducing other error factors caused by opening the drive.
The method and apparatus in accordance with the present invention solves the aforementioned problem and other problems by using control mechanisms and read/write apparatuses within a disc drive to create a microtrack that is used to probe the magnetic sensitivity of each portion of the magnetic stripe within the magneto-resistive head of the disc drive. More specifically, a method can be executed to produce a signal-strength profile for a magneto-resistive stripe, by first selecting a target track, and then recording a test signal along the target track. Next, the target track is trimmed to create a microtrack wherein the microtrack has a microtrack width less than the stripe width. The microtrack thus formed has a first circumferential edge and a second circumferential edge. After the creation of the microtrack, the magneto-resistive stripe is scanned at various radial locations between the first and second circumferential edges of the microtrack. Finally, a signal strength is determined for each of the detected signals.
A test system composed of a computer, an oscilloscope, and a disc drive under test can cooperate to perform the above-described steps, thereby collecting the data necessary to create a signal-strength profile for a magneto-resistive stripe within the disc drive under test.